Why is Glycerine Used in Watercolours?

Glycerin is commonly used in watercolor medium recipes as a plasticizer. A plasticizer is a substance that is added to a material to increase its flexibility and reduce brittleness. In the case of watercolor paint, glycerin helps to make the paint more flexible and less prone to cracking as it dries on the paper.

Glycerin is also a humectant, which means it helps to regulate the moisture content of the paint and prevent it from becoming too dry. This can help to keep the pigments from losing their vibrancy and can also make the paint easier to rewet and manipulate.

When using glycerin in a watercolor medium recipe, it's important to use a pure, pharmaceutical-grade glycerin to ensure the best results. Additionally, it's a good idea to use a moderate amount of glycerin, as too much can make the paint too flexible and result in a loss of control when painting.